using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.UIElements;

public class TabbedView : VisualElement
{
    public new class UxmlFactory : UxmlFactory<TabbedView, UxmlTraits> { }

    private const string k_styleName = "TabbedView";
    private const string s_UssClassName = "unity-tabbed-view";
    private const string s_ContentContainerClassName = "unity-tabbed-view__content-container";
    private const string s_TabsContainerClassName = "unity-tabbed-view__tabs-container";

    private readonly VisualElement m_TabContent;
    private readonly VisualElement m_Content;

    private readonly List<TabButton> m_Tabs = new List<TabButton>();
    private TabButton m_ActiveTab;

    public override VisualElement contentContainer => m_Content;

    public TabbedView()
    {
        AddToClassList(s_UssClassName);

        styleSheets.Add(Resources.Load<StyleSheet>($"Styles/{k_styleName}"));

        m_TabContent = new VisualElement();
        m_TabContent.name = "unity-tabs-container";
        m_TabContent.AddToClassList(s_TabsContainerClassName);
        hierarchy.Add(m_TabContent);

        m_Content = new VisualElement();
        m_Content.name = "unity-content-container";
        m_Content.AddToClassList(s_ContentContainerClassName);
        hierarchy.Add(m_Content);

        RegisterCallback<AttachToPanelEvent>(ProcessEvent);
    }

    public void AddTab(TabButton tabButton, bool activate)
    {
        m_Tabs.Add(tabButton);
        m_TabContent.Add(tabButton);

        tabButton.OnClose += RemoveTab;
        tabButton.OnSelect += Activate;

        if (activate)
        {
            Activate(tabButton);
        }
    }

    public void RemoveTab(TabButton tabButton)
    {
        int index = m_Tabs.IndexOf(tabButton);

        // If this tab is the active one make sure we deselect it first...
        if (m_ActiveTab == tabButton)
        {
            DeselectTab(tabButton);
            m_ActiveTab = null;
        }

        m_Tabs.RemoveAt(index);
        m_TabContent.Remove(tabButton);

        tabButton.OnClose -= RemoveTab;
        tabButton.OnSelect -= Activate;

        // If we closed the active tab AND we have any tabs left - active the next valid one...
        if ((m_ActiveTab == null) && m_Tabs.Any())
        {
            int clampedIndex = Mathf.Clamp(index, 0, m_Tabs.Count - 1);
            TabButton tabToActivate = m_Tabs[clampedIndex];

            Activate(tabToActivate);
        }
    }

    private void ProcessEvent(AttachToPanelEvent e)
    {
        // This code takes any existing tab buttons and hooks them into the system...
        for (int i = 0; i < m_Content.childCount; ++i)
        {
            VisualElement element = m_Content[i];

            if (element is TabButton button)
            {
                m_Content.Remove(element);

                if (button.Target == null)
                {
                    string targetId = button.TargetId;

                    button.Target = this.Q(targetId);
                }
                AddTab(button, false);
                --i;
            }
            else
            {
                element.style.display = DisplayStyle.None;
            }
        }

        // Finally, if we need to, activate this tab...
        if (m_ActiveTab != null)
        {
            SelectTab(m_ActiveTab);
        }
        else if (m_TabContent.childCount > 0)
        {
            m_ActiveTab = (TabButton)m_TabContent[0];

            SelectTab(m_ActiveTab);
        }
    }

    private void SelectTab(TabButton tabButton)
    {
        VisualElement target = tabButton.Target;

        tabButton.Select();
        if (target != null)
            Add(target);
    }

    private void DeselectTab(TabButton tabButton)
    {
        VisualElement target = tabButton.Target;

        if (target != null)
            Remove(target);
        tabButton.Deselect();
    }

    public void Activate(TabButton button)
    {
        if (m_ActiveTab != null)
        {
            DeselectTab(m_ActiveTab);
        }

        m_ActiveTab = button;
        SelectTab(m_ActiveTab);
    }
}